1. Field of the Invention
The present invention relates to an automatic transmission. More particularly, the present invention relates to a control apparatus for an automatic transmission and a control method that minimizes distortion of a drive shaft that is generated by thrust of a vehicle when parking on a sloped road.
2. Description of Related Art
When a vehicle that has an automatic transmission is parked, the shift lever is located in a parking mode (P range).
FIG. 5 is a cross-sectional view of parking apparatus that is applied to an automatic transmission.
Referring to FIG. 5, a parking apparatus of an automatic transmission includes a detent lever 104 that rotates as a shift lever 102 selects a parking mode, a parking rod 106 that is connected to a side of the detent lever 104 and moves in a straight line according to a rotation of the detent lever 104, a parking pawl lever 110 that is rotatably mounted at a support bracket 108 and rotates when the parking rod 106 moves in a straight line, and a parking gear 112 that is installed in a planetary gear set of the automatic transmission and on which latch grooves 114 are formed in the outer circumferential surface at regular intervals so that the parking pawl lever 110 may be combined thereto.
A detent spring 116, which blocks the detent lever 104 during rotation of the detent lever 104, is formed at a side of the detent lever 104, a rod spring 118 that provides elastic force is mounted on the parking rod 106, and a roller 120 that pushes up the parking pawl lever 110 when the parking rod 106 moves in a straight line is mounted at an end portion of the parking rod 116.
In the middle of the parking pawl lever 110, a hinge connection portion 130 that is rotatably supported in the automatic transmission is formed, and a return spring 132 that reinstates a parking sprag is formed at the hinge connection portion 130.
A sloped surface that contacts the roller 120 is formed at an end portion of the parking pawl lever 110, and an engagement protrusion 122 that is engaged with the latch groove 114 of the parking gear 112 is formed at the other end portion of the parking pawl lever 110.
In a parking apparatus of an automatic transmission that is formed in this way, when a driver places the shift lever 102 in the parking mode, the detent lever 104 rotates, the parking rod 106 connected with the detent lever 104 moves in a straight line, and the roller 120 mounted at the end portion of the parking rod 106 enters into the slanted surface of the parking pawl lever 110 to push up an end portion of the parking pawl lever 110.
Then, the engagement protrusion 122 formed at the end portion of the parking pawl lever 110 moves downward and is combined with the latch groove 114 of the parking gear 112 to fix the parking gear 112 and maintained the parked state.
Also, when the shift lever 102 moves from the parking position to another position, the parking rod 106 is reinstated by the rod spring 118 and the parking pawl lever 110 is reinstated by elastic force of the return spring 132 so that the engagement protrusion 122 cannot be engaged and restricts the parked state.
When a driver operates an automatic transmission vehicle, the driver often parks the vehicle on a sloped road. If the shift lever is placed in the parking mode after the vehicle is parked on the sloped road, the vehicle is thrust backward or forward by the weight of the vehicle.
For example, if a rear-wheel drive vehicle parked on the slope road is thrust backward, torque is exerted on the wheel by the weight of vehicle so that the parking gear, a drive shaft, and a wheel drive shaft are sequentially distorted and energy is accumulated.
Therefore, the stress on each of the elements is dispersed and the elements are deformed by the accumulated energy, so the durability is deteriorated.
Also, when the shift lever is released from the parking mode (P range), to run in the energy-accumulated state by the sequential distortions, the accumulated energy is released and that increases the distortion vibration of the driving system, and serious impact and vibration are generated in a torque rear differential such that much noise is transferred into the vehicle through the vehicle body such that the product quality is deteriorated.
As shown in FIG. 6, experiments show that when the parking mode is released in the parked state on flat road, any special impact, vibration or noise is not generated. However, FIG. 7 shows that when the parked state on the sloped road is released, substantial distortion motion of the rear differential, torque vibration of the driving system, and interior noise are created.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.